Deltaic Progradation During Maximum Marine Transgression, the Heebner Shale Member of the Oread Limestone Formation (Virgilian), Southeast Kansas and Northeast Oklahoma

W. Yang, M. Bruemmer, and M. Turnerwilliams
Department of Geology, Wichita State University, Wichita, KS ([email protected])

The widespread Heebner Shale of the Pennsylvanian Oread Cyclothem was deposited on the Kansas shelf and adjacent basins in a paleoequatorial belt during a maximum marine flooding. It overlies persistent and thin (~50 cm) transgressive Leavenworth Limestone and underlies persistent but variably thick (0–8 m) regressive Plattsmouth Limestone along a 120-km outcrop in southeastern Kansas and northeast Oklahoma. In the northern and central outcrop belt, the Heebner is thin (1–3 m) and dominantly black with abundant phosphatic nodules, representing a condensed section deposited on an anoxic to dysaerobic starved shelf. In the southern belt, however, the Heebner thickens to 30 m over a distance of 30 km and consists of upward-coarsening green-gray plant-rich shale, siltstone, and sandstone, deposited in prodeltaic to delta-front environments. The delta was sourced by the Ouachita thrustbelts and prograded across the filled Arkoma Basin during maximum flooding and sea-level highstand. The sediment yield in the source area was copious because of efficient weathering due to the humid equatorial climate and the high topographic relief. Sediment transport was efficient due to the low wave energy in the inland sea, the large river discharge, and the steep topographic gradient between the source area and depositional site. The large river runoff also contributed to shelf anoxia by freshwater capping dense oceanic water, causing stagnant oceanic circulation. The findings are not predicted by the depositional sequence model and signify the interplay of oceanic and climatic processes, sediment yield and sediment supply, and topography of drainage basins during sequence formation.

AAPG Search and Discovery Article #90903©2001 AAPG Mid-Continent Meeting, Amarillo, Texas